add buildbot extension for autoscaling nix builders

buildbot-ext/buildbot_autoscale_ext/settings.py

@@ -0,0 +1,14 @@
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class AutoscaleSettings:
+    daemon_socket: str
+    system_property: str = "system"
+    default_system: str = "x86_64-linux"
+    reserve_timeout_seconds: int = 900
+    poll_interval_seconds: float = 5.0
+    retry_max_attempts: int = 5
+    retry_base_seconds: float = 0.5
+    retry_max_seconds: float = 5.0
+    release_on_finish: bool = True